School of Food and Biological Engineering, Jiangsu University, Zhenjiang, P.R. China.
Department of Botany, Shah Abdul Latif University, Khairpur, Pakistan.
J Food Biochem. 2019 Apr;43(4):e12809. doi: 10.1111/jfbc.12809. Epub 2019 Feb 18.
The study aims to determine drying of sweet potatoes using multifrequency ultrasound (US) pretreatments (20, 40, and 60 kHz) at three different infrared (IR) drying temperatures (60, 70, and 80°C) and evaluate the phytochemical and textural quality of the dried product. Drying time was significantly decreased in moderate US frequency (40 kHz) at 70°C with the increasing drying temperature. Comparing to the fresh samples, the dried samples showed the highest amount of phytochemical contents. The antioxidant activity of the samples increased especially at 60 kHz and 80°C, while US-IR treatments shown a positive impact on total carotenoids contents and β-carotene. For phenolic compounds, Ellagic acid and Rutin were quantified in higher amount while Quercetin-3-rhamnoside and Quercetin 3-β-D-glucoside were two new compounds identified for the first time in sweet potatoes. FTIR spectra showed the successful synthesis of OH group and phenolics in samples treated with the US at 20 kHz. PRACTICAL APPLICATIONS: This study investigated the effects of multifrequency ultrasound with different infrared drying temperatures. The study provides evidence that infrared drying application in synergy with ultrasonic pretreatments can improve drying efficiency and food quality much better than using each method alone. Total phenolic contents and total flavonoid contents remained stable at US 40 kHz and 60°C conditions. The findings showed that moderate ultrasound frequency (40 kHz) at 60°C improved phytochemical properties while antioxidant activities showed better preservation response at 80°C with 60 kHz. In addition, the samples treated with the same US treatment at 40 kHz showed less cell breakage in SEM analysis.
本研究旨在利用多频超声（20、40 和 60 kHz）预处理，在三种不同的红外（IR）干燥温度（60、70 和 80°C）下对甘薯进行干燥，并评估干燥产品的植物化学和质地质量。在 70°C 时，中等超声频率（40 kHz）下的干燥时间显著缩短，且随着干燥温度的升高而增加。与新鲜样品相比，干燥样品表现出最高的植物化学物质含量。抗氧化活性在 60 kHz 和 80°C 时尤其增加，而超声-IR 处理对总类胡萝卜素含量和β-胡萝卜素有积极影响。对于酚类化合物，鞣花酸和芦丁的含量较高，而槲皮素-3-鼠李糖苷和槲皮素 3-β-D-葡萄糖苷是首次在甘薯中鉴定出的两种新化合物。傅里叶变换红外（FTIR）光谱显示，在 20 kHz 下用超声处理的样品中成功合成了 OH 基团和酚类化合物。
本研究调查了不同红外干燥温度下多频超声的影响。研究结果表明，与单独使用每种方法相比，红外干燥与超声预处理联合应用可以更好地提高干燥效率和食品质量。总酚含量和总黄酮含量在 40 kHz 和 60°C 的超声条件下保持稳定。结果表明，在 60°C 时，中等超声频率（40 kHz）可改善植物化学特性，而在 80°C 时，60 kHz 可更好地保持抗氧化活性。此外，在 SEM 分析中，在相同的 40 kHz 超声处理下，样品的细胞破裂程度较低。
